Tides and Tidal Streams Flashcards

How would you find the height of tide at a secondary port?

Answer: Apply the time and height differences listed in the tide tables to the standard port predictions

Secondary port predictions are calculated by applying published time differences and height differences (or ratios) to the predictions for the associated standard port, as listed in nautical almanacs.

What is a 'tidal stream atlas' used for?

Answer: Showing the direction and rate of tidal streams at hourly intervals relative to high water at a standard port

A tidal stream atlas shows arrows indicating the direction and rate (in knots, for springs and neaps) of tidal streams at hourly intervals, referenced to HW at a standard port.

What does 'drying height' on a chart indicate?

Answer: The height of the seabed above chart datum — these areas are exposed (dry) at low water

A drying height (shown underlined on charts) indicates how far the seabed rises above chart datum. These areas are covered at high water but exposed at low water.

When using tidal diamonds on a chart, what do the columns for spring and neap rates tell you?

Answer: The speed of the tidal stream in knots at mean springs and mean neaps for each hour relative to HW at the reference port

Tidal diamond tables give the direction and rate of the tidal stream for each hour relative to HW at the standard port, with separate rate columns for mean spring and mean neap conditions.

What is the 'range' of a tide?

Answer: The vertical difference between high water and low water

Tidal range is the vertical difference in height between consecutive high water and low water. Spring tides have a larger range than neap tides.

At what point in the tidal cycle does the tidal stream typically turn?

Answer: Approximately at high and low water, though the exact time varies by location

Tidal streams typically change direction (turn or 'slack') approximately at high and low water, but the exact timing varies by location. In some areas, the stream may turn well before or after HW/LW.